1. Field of the Invention
This invention relates to vehicular transmissions such as step ratio automatic transmissions.
2. Background Art
Today's step ratio automatic transmissions use hydraulics to power the ratio change, dampen NVH, power coupling/decoupling, and providing lubrication and cooling. This is achieved with the use of a torque converter (for coupling/decoupling power, multiplying torque, and NVH dampening), an oil pump, valve body (or hydraulic logic), and friction-type clutches (bands and frictions as shown in FIG. 1).
The torque converter provides fluid coupling between the engine and the transmission. A typical torque converter comprises: an impeller which is rigidly connected to the torque converter housing; a turbine which is splined to the input shaft (turbine shaft) of the transmission; and a stator which includes a one-way clutch. An inner race of the one-way clutch is splined to a stationary shaft attached to the transmission.
The transmission oil pump is used to circulate oil and provide pressure for hydraulic operation. The pump is driven by the torque converter shell and rotates with the engine. Fluid is drawn from a sump through a filter and is distributed to the various transmission hydraulic systems.
The hydraulic control components of a transmission include an electro/hydraulic valve body. The valve body assembly is the main shift control element in the transmission. In non-EH (i.e., electro/hydraulic) transmissions the valve body was only hydraulically controlled. In current EH transmissions the valve body is similar in design, but now also houses a number of shift solenoids which are controlled by a transmission control module.
The valve body consists of a number of sub-assemblies. Each sub-assembly contains a number of spool valves which are hydraulically controlled. Most spool valves are opposed by spring pressure. The spool valves are used to direct hydraulic fluid flow to the various shift elements in the transmission. There is also a manual valve which is connected to the shift assembly by a cable. The manual valve allows the drivers to select the basic operating mode (or ratio).
The valve body is responsible for:
regulating main pressure;
controlling fluid flow to shift elements for upshifts and downshifts;
providing for manual operation by driver via manual valve;
reverse lockout;
failsafe operation;
shift comfort through:                overlap shift control; and        pressure accumulators;        
torque converter control; and
distribution of lubrication.
Multi-Plate Friction-Type Clutches and Brakes
Clutches and brakes are used to drive or hold members of a planetary gear set, respectively. As a general rule, multi-plate clutches connect one planetary member to another. Multi-plate brakes connect a planetary member to the transmission case to hold it stationary.
The clutches and brakes consist of a number of friction discs and steel discs. The friction discs are coated with a friction material and have engaging lugs (splines) on the inner perimeter. The steel discs are steel on both sides and have engaging lugs located on the outer perimeter. The engaging lugs on the friction discs are usually engaged with a planetary member. The engaging lugs on the steel discs are usually engaged with the clutch piston housing.
In addition to the friction and steel discs, there is also an apply piston, housing and return spring. Once hydraulic fluid is applied to the clutch assembly, the friction discs and steel discs will be locked together. Once hydraulic pressure is released, the return spring will cause the clutch piston to return to its rest position which will unlock the clutch assembly.
A band-type brake is used for some applications. The brake band is a circular band with friction material bonded to the inner surface. The band wraps around a particular planetary component (clutch drum) and locks that component to the transmission case. The brake band is applied and released by the clutch apply piston.
In order to carry out a shift in ratio, fluid needs to be applied or released from the multi-plate clutch (or brake). The following method occurs:
1. Fluid from a shift valve in the valve body is applied to the clutch assembly.
2. Fluid pressure builds behind the apply piston and overcomes the resistance from diaphragm spring.
3. The friction and steel discs are compressed together and become locked, preventing any slippage between them.
4. Two planetary members are now locked together.
5. When fluid pressure is released, the steel and friction discs are allowed to unlock.
This method has had some advantages. The power density is very high using hydraulics to clamp clutches and to multiply torque. Hydraulic systems have proven to have good dampening characteristics and smooth shift capability. It is also a natural way to lubricate the components in the transmission and to carry away heat from torque converters, pumps, gear sets, bearings, etc.
However, there are a few disadvantages. The first is efficiency. The pump is always on and pumping oil whenever the engine is running. When a friction element is turned on, power is used to maintain the clamping pressure of that friction element.
The slipping of the torque converter is also a significant source of loss and the open friction elements in the transmission provide drag and thus losses also. Another disadvantage is the complexity of these components. Clutches, pumps, torque converters, and valve bodies are the most likely components to have issues and thus drive warranty cost and negatively impact upon customer satisfaction. These components also tend to be the most expensive components in the transmission.
A typical one-way clutch consists of an inner ring, an outer ring and a locking device between the two rings. The one-way clutch is designed to lock in one direction and to allow free rotation in the other direction. Two types of one-way clutches often used in vehicular, automatic transmissions include:                Roller type which consists of spring loaded rollers between the inner and outer race of the one-way clutch. (Roller type is also used without springs on some applications); and        Sprag type which consists of asymmetrically shaped wedges located between the inner and outer race of the one-way clutch.        
The one-way clutches are typically used in the transmission to prevent an interruption of drive torque (i.e., power flow) during certain gear shifts and to allow engine braking during coasting. Also there is a one-way clutch in the stator of the torque converter as previously mentioned.
U.S. Pat. No. 5,927,455 discloses a bi-directional overrunning pawl-type clutch having a driving member mounted for power rotation, a driven member mounted for rotation adjacent the driving member, with each of the driving and driven members having pawl engaging shoulders, and a plurality of rigid pawls interposed between the driving and driven members. A control element is mounted for shifting movement between the driving and driven members to control the position of the pawls which are yieldably biased toward positions of engagement extending between the driving and driven members to produce driving engagement therebetween. The control element is shiftable to various positions to permit driving and overrunning in one direction or driving and overrunning in the opposite direction dependent upon the direction of rotation of the driving member.
U.S. Pat. No. 6,244,965 discloses a planar overrunning coupling for transfer of torque from a driving member to a driven member in one direction and which permits freewheeling motion between the members upon a torque reversal. The coupling includes coupling plates situated in close proximity with a strut retainer plate disposed between them, one plate being connected to the driving member and the other plate being connected to the driven member, each plate having strut recesses, a series of struts located in the recesses of one plate so that each strut may be pivoted, thereby allowing the struts to engage the companion recesses in the other coupling plate. The retainer has angularly spaced apertures that register with the struts to permit pivotal movement of the struts when the retainer plate is in one rotary position. The retainer plate, when it is in a second rotary position, prevents pivotal motion of the struts, thereby permitting freewheeling relative motion of the coupling plates.
U.S. Pat. No. 6,290,044 discloses a selectable one-way clutch assembly for use in an automatic transmission comprising a strut plate rotatable about a central hub and having pockets and struts mounted therein for pivotable rotation. A selecting plate concentrically located about an activator hub has teeth extending axially inboard and configured to fit in the apertures in an activator plate. A turning device is selectively operable to activate one-way clutching mode by rotating the pin of a control plate to disengage selecting cams and displace selecting plate teeth inboard beyond the inboard face of the activator plate wherein the struts catch the teeth when the strut plate assembly is rotated in a clutching direction. The catching ends of the struts are cammed in the pockets by ramped camming ends of the teeth when the strut plate assembly is rotated in the opposing direction, thereby allowing freewheeling of the strut plate in the overrun direction.
U.S. Pat. No. 7,258,214 discloses an overrunning coupling assembly and a method of controlling the engagement of planar first and second members wherein two sets of opposed engaging struts are applied with one motion of a single control plate or member. The planar first and second members have inside surfaces extending generally normal to a first axis. The assembly includes free-floating, forward keys and free-floating, reverse keys opposed to the forward keys. The forward and reverse keys are movable between a notch-engaging, engaged position and a disengaged position in which the second member is permitted to free-wheel relative to the first member. The planar control member is disposed between the first and second surfaces and is controllably rotatable about the first axis between first and second angular positions relative to the first member.
U.S. Pat. No. 7,344,010 discloses an overrunning coupling assembly and a method of controlling the engagement of planar first and second members wherein the assembly includes clustered pawls and their respective pawl-holding portions. The planar first and second members have inside surfaces extending generally normal to a first axis. The pawls include a forward set of free-floating pawls and a reverse set of free-floating, clustered pawls. The forward and reverse sets of pawls are movable between a notch-engaging, engaged position and a disengaged position. Because of the clustering, a control element, disposed between the first and second surfaces, need not be fully circular and is controllably rotatable about the first axis between first and second angular positions relative to the first member.
Published patent application US 2006/0278487 discloses an overrunning radial coupling assembly or clutch and a method of controlling the engagement of inner and outer plates or members of the assembly wherein adjacent engaging radial locking pawls are selectively controlled by a single, rotatable control plate or element to obtain full lock, one-way lock and one-way overrun conditions. The assembly includes free-floating, forward pawls and free-floating, reverse pawls adjacent to their respective forward pawls. The forward and reverse pawls are movable between a notch-engaging, engaged position (i.e., full lock condition) and a disengaged position in which the outer member is permitted to free-wheel relative to the inner member in the one-way overrun condition in one direction about a first axis and the outer member is locked to the inner member in the one-way lock condition in the opposite direction. A number of different embodiments of the assembly and method are provided.
U.S. Pat. No. 6,953,409 discloses a two-mode, compound-split, electra-mechanical transmission which utilizes an input member for receiving power from an engine, and an output member for delivering power from the transmission. First and second motor/generators are operatively connected to an energy storage device through a control for interchanging electrical power among the storage device, the first motor/generator and the second motor/generator. The transmission employs three planetary gear sets. Each planetary gear arrangement utilizes first, second and third gear members. Moreover, one gear member of the first or second planetary gear set is operatively connected to the input member, and one gear member of the third planetary gear set is selectively connected to ground. A lock-up clutch selectively locks two of the planetary gear sets in a 1:1 ratio.
U.S. Pat. No. 7,256,510 discloses an electro-mechanical transmission having only a single motor/generator, at least one differential gear set and two torque-transmitting mechanisms. A first of the torque-transmitting mechanisms is selectively engageable to establish a first continuously variable operating mode and a second of the torque-transmitting mechanisms selectively engageable to establish a second continuously variable operating mode and a synchronous shift between the two operating modes is achievable. A method of control is provided in which vehicle operating characteristics are analyzed to identify a target operating state in terms of operating mode and ratio based on the available motor torque and motor power and on maximizing energy efficiency. The transmission is controlled to approach this operating mode as closely as possible and the diverge away from the optimum torque operating with zero net battery use as the battery charge of the battery connected with the motor/generator accumulates or depletes.
For purposes of this application, the term “coupling” should be interpreted to include clutches or brakes wherein one of the plates is drivably connected to a torque delivery element of a transmission and the other plate is drivably connected to another torque delivery element or is anchored and held stationary with respect to a transmission housing. The terms “coupling,” “clutch” and “brake” may be used interchangeably.